DOI: 10.1148/rg.232025089
(Radiographics. 2003;23:403-424.)
© RSNA, 2003
MR Imaging of Common and Uncommon Large Pelvic Masses1
Janio Szklaruk, MD, PhD,
Eric P. Tamm, MD,
Haesun Choi, MD and
Vithya Varavithya, MD
1 From the Department of Diagnostic Radiology, Division of Diagnostic Imaging, University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030. Received May 3, 2002; revision requested June 10 and received October 10; accepted October 10. Address correspondence to J.S. (e-mail: jszklaru@di.mdacc.tmc.edu).
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Abstract
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Magnetic resonance (MR) imaging is often used in the detection and staging of large pelvic masses. Many large masses in the female pelvis arise from the reproductive organs (eg, uterus, cervix, ovaries, fallopian tubes). In addition, these masses may arise from the gastrointestinal system, urinary system, adjacent soft tissues, peritoneum, or retroperitoneum or from metastases. The majority of large masses in the female pelvis represent such commonly encountered entities as uterine fibroid tumor, dermoid tumor, ovarian cyst, and ovarian cancer. However, uncommon pelvic masses such as mesothelioma, adenocarcinoma, carcinosarcoma, leiomyosarcoma, and desmoid tumor may also be seen. Thus, the differential diagnosis for female pelvic masses is extensive. However, the site of origin, MR imaging characteristics, and clinical history may all help narrow the differential diagnosis. Although with large tumors it may not always be possible to determine the site of origin or distinguish between various tumors at radiology, familiarity with the clinicopathologic and MR imaging features of common and uncommon pelvic masses is important for diagnosis and treatment.
© RSNA, 2003
Index Terms: Gastrointestinal system, MR, 70.1214 • Gastrointestinal system, neoplasms, 70.31, 70.32 • Genitourinary system, MR, 85.1214 • Genitourinary system, neoplasms, 85.31, 85.32 • Pelvis, MR, 70.1214, 85.1214 • Pelvis, neoplasms, 70.31, 70.32, 85.31, 85.32
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Identify the clinical and pathologic features of various pelvic masses.
- Describe the MR imaging features of various pelvic masses.
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Introduction
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During routine clinical practice, radiologists often must evaluate a wide range of pelvic diseases, one of the most problematic being large (>5-cm) masses. Large pelvic masses in women may originate from the uterus, cervix, ovaries, fallopian tubes, peritoneum, or retroperitoneum. Magnetic resonance (MR) imaging is commonly used in the work-up of such lesions. Often the diagnosis can be suggested on the basis of tumor location and anatomic landmarks. These landmarks include the organ of origin (uterus, cervix, ovaries, intestinal tract), relationship to vasculature, peritoneal or extraperitoneal involvement, and lateral pelvic wall involvement. Determining tumor location is much more difficult when the tumor exceeds 5 cm in diameter. On the other hand, this largeness is sometimes useful for staging. The majority of large pelvic masses in female patients represent such commonly encountered entities as uterine fibroid tumors, dermoid tumors, ovarian cysts, and ovarian cancer. However, uncommon pelvic masses such as mesothelioma, adenosarcoma, carcinosarcoma, leiomyosarcoma, and desmoid tumor may also be encountered. Establishing the correct diagnosis and accurately staging these tumors is important, particularly when surgical resection can be an option. In this article, we discuss and illustrate the MR imaging characteristics, staging, and clinicopathologic features of various common and uncommon pelvic masses.
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Uterine Neoplasms
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Large pelvic masses may originate from the uterus. Such tumors may be classified as endometrioid or mesenchymal-type tumors.
Endometrial Cancer
The most common endometrioid tumor of the uterus—and the most common cancer of the female genital tract—is endometrial cancer. Patients typically present between the 2nd and 8th decades of life, with a mean age at presentation of 59 years. The most common clinical manifestation is abnormal vaginal bleeding (1,2). At gross examination, the tumor may appear as an exophytic (and sometimes large) mass or as diffuse endometrial thickening. On cut section, the tumor has a shaggy, gray-white ulcerated surface with scattered regions of hemorrhage or necrosis. Invasive tumors infiltrate the myometrium. At histologic analysis, these tumors are composed of well-formed glands and may demonstrate masses of solid epithelium (2,3). The staging of endometrial carcinoma is based on extension of the primary tumor, adenopathy, and metastases (Table 1). Most women with endometrial cancer have stage I disease (4). MR imaging is useful not only in identifying the tumor but also in assessing myometrial invasion, adenopathy, and metastases. These tumors have intermediate to low signal intensity on T1-weighted MR images and low signal intensity on T2-weighted images (Fig 1). Dynamic contrast material–enhanced MR images are sometimes used to evaluate pelvic masses (Fig 2). At early dynamic contrast-enhanced MR imaging, endometrial carcinoma enhances less than myometrium; on delayed scans, there is less distinction in enhancement (5,6). MR imaging has been reported to be helpful in the staging of endometrial cancer (Table 1) (7). The differential diagnosis for endometrial cancer may include cervical cancer, endometrial polyps, and mesenchymal tumors of the uterus. Distinguishing between these entities is easier in smaller tumors. Treatment of endometrial cancer is typically hysterectomy with radiation therapy. In cases of advanced disease, the treatment of choice is local radiation therapy and chemotherapy (1,2). The 5-year survival rate for patients with endometrial cancer is 81%–94% for stage I disease, 67%–77% for stage II, 32%–41% for stage III, and 5%–20% for stage IV disease (4).
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Figure 1a. Endometrial cancer in a 61-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates an endometrial mass with heterogeneous signal intensity. (b) Axial spin-echo T1-weighted MR image obtained after the intravenous administration of gadopentetate dimeglumine shows the mass with heterogeneous enhancement.
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Figure 1b. Endometrial cancer in a 61-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates an endometrial mass with heterogeneous signal intensity. (b) Axial spin-echo T1-weighted MR image obtained after the intravenous administration of gadopentetate dimeglumine shows the mass with heterogeneous enhancement.
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Figure 2a. High-grade uterine sarcoma in a 61-year-old woman. Sagittal unenhanced gradient-echo MR image of the uterus (a) and contrast-enhanced gradient-echo MR images of the uterus obtained 15 (b) and 35 (c) seconds after intravenous administration of gadopentetate dimeglumine show enhancement of a uterine neoplasm.
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Figure 2b. High-grade uterine sarcoma in a 61-year-old woman. Sagittal unenhanced gradient-echo MR image of the uterus (a) and contrast-enhanced gradient-echo MR images of the uterus obtained 15 (b) and 35 (c) seconds after intravenous administration of gadopentetate dimeglumine show enhancement of a uterine neoplasm.
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Figure 2c. High-grade uterine sarcoma in a 61-year-old woman. Sagittal unenhanced gradient-echo MR image of the uterus (a) and contrast-enhanced gradient-echo MR images of the uterus obtained 15 (b) and 35 (c) seconds after intravenous administration of gadopentetate dimeglumine show enhancement of a uterine neoplasm.
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Mesenchymal Tumors
Mesenchymal tumors are subclassified as smooth muscle, endometrial stromal, or mixed epithelial-mesenchymal tumors (3).
Leiomyoma.—
The most common uterine neoplasm—and the most common smooth muscle tumor of the uterus—is leiomyoma. Leiomyomas are most common in middle-aged women, with a prevalence of 20%–30% in patients over 30 years old. The clinical signs and symptoms depend on the size, location, and number of leiomyomas. The most common clinical manifestations are pain and abnormal vaginal bleeding. At gross examination, the tumor is white to tan and is sharply demarcated from the myometrium (3,8,9). Leiomyomas consist of spindle-shaped cells in a trabecular pattern, creating a whorled appearance (3,9). The amount of fibrous tissue, collagen, and extracellular matrix is variable. The tumors are classified as intramural, cervical, submucosal, or subserosal depending on their location. On T2-weighted MR images, leiomyomas are typically well demarcated and have low signal intensity but can have a variable appearance depending on the presence of cystic degeneration, necrosis, hemorrhage, or cellular-type leiomyoma (Fig 3). On T1-weighted MR images, these tumors are isointense relative to the myometrium and demonstrate enhancement after administration of contrast material (Fig 3). Treatment for symptomatic patients is typically hysterectomy. Other treatments include embolization, hormonal therapy, and laparoscopic myomectomy. The differential diagnosis for leiomyoma includes adenomyoma, leiomyosarcoma, and lipoleiomyoma.
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Figure 3a. Fibroid tumors in a 50-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates intramural fibroid tumors. The anterior tumor has heterogeneous signal intensity, whereas the posterior and superior tumors have the more typical low signal intensity. (b) Sagittal contrast-enhanced gradient-echo T1-weighted MR image demonstrates enhancement of the tumors.
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Figure 3b. Fibroid tumors in a 50-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates intramural fibroid tumors. The anterior tumor has heterogeneous signal intensity, whereas the posterior and superior tumors have the more typical low signal intensity. (b) Sagittal contrast-enhanced gradient-echo T1-weighted MR image demonstrates enhancement of the tumors.
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Endometrial Stromal Sarcoma.—
Like leiomyomas, endometrial stromal sarcomas are mesenchymal tumors. They account for less than 10% of uterine sarcomas. The mean age at presentation is 42–53 years. Patients most commonly present with abnormal vaginal bleeding and pain. Endometrial stromal sarcomas are typically soft, tan, and polypoid and may fill the endometrial cavity (3). About 50% of these tumors appear well circumscribed. Hemorrhage and necrosis are frequently present (9). Histologic grades include stromal nodule (benign), low-grade, high-grade, and undifferentiated. Microscopic examination reveals proliferative-phase stromal cells, with little variation (3). The degree of cell atypia depends on the histologic grade. The staging of uterine sarcomas is similar to that of endometrial cancer (Table 1): Stage I uterine sarcoma is limited to the body of the uterus, stage II has spread to the cervix, stage III has spread outside the uterus but remains within the pelvis, and stage IV uterine sarcoma has metastasized. MR imaging is useful in staging these tumors by allowing assessment of spread to adjacent organs and lymph nodes. The MR imaging appearance of these tumors is similar to that of other pelvic masses. The tumor is isointense relative to myometrium on T1-weighted images, is hyperintense on T2-weighted images, and demonstrates heterogeneous enhancement on contrast-enhanced images (Fig 4) (10). Treatment is typically hysterectomy. Other treatment options include radiation therapy and chemotherapy. The differential diagnosis includes endometrial carcinoma of the uterus. The overall 5-year survival rate is 62% (11).
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Figure 4a. Endometrial stromal sarcoma in a 35-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates a high-signal-intensity mass in the endometrial canal that originates from the corpus uteri. (b) Axial contrast-enhanced spin-echo T1-weighted MR image shows enhancement of the mass.
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Figure 4b. Endometrial stromal sarcoma in a 35-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates a high-signal-intensity mass in the endometrial canal that originates from the corpus uteri. (b) Axial contrast-enhanced spin-echo T1-weighted MR image shows enhancement of the mass.
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Adenosarcoma.—
Adenosarcoma is an uncommon mesenchymal tumor. It is a malignant tumor that contains benign epithelial components and sarcomatous stroma. Adenosarcoma represents 8% of all uterine sarcomas. The most common presenting symptom is abnormal vaginal bleeding, and the mean age at presentation is 58 years. At gross examination, the tumor appears as a well-demarcated polypoid mass that arises in the endometrium and protrudes through the cervical os (3). Hemorrhage, myometrial invasion, and necrosis may be present. At histologic analysis, the tumor consists of stromal components that may include uterine elements (homologous) or elements not found in the uterus (heterologous) (3). Homologous elements include endometrial stromal cells, smooth muscle cells, and fibroblasts. Heterologous elements include striated muscle, cartilage, osteoid, and fat. The tumor is typically homologous. At MR imaging, adenosarcoma usually manifests as a large, multiseptated cystic mass with multiple heterogeneous solid components that fill the endometrial cavity (12). The staging is the same as for endometrial stromal sarcoma (Table 1). The solid component has low signal intensity on T2-weighted MR images and enhances on contrast-enhanced T1-weighted images (Fig 5). Treatment is typically total abdominal hysterectomy with bilateral salpingo-oophorectomy, followed by postoperative adjuvant pelvic radiation therapy. The 5-year survival rate is estimated at 10%–25% (13).
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Figure 5a. Pelvic adenosarcoma in a 47-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image reveals a mass with heterogeneous signal intensity. (b) Axial contrast-enhanced spin-echo T1-weighted MR image demonstrates enhancement of the mass.
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Figure 5b. Pelvic adenosarcoma in a 47-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image reveals a mass with heterogeneous signal intensity. (b) Axial contrast-enhanced spin-echo T1-weighted MR image demonstrates enhancement of the mass.
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Carcinosarcoma.—
Carcinosarcoma is the most common uterine sarcoma. It represents less than 2% of all uterine tumors. Patients present between the 3rd and 8th decades of life, with a mean age of 65 years. Clinical manifestations include vaginal bleeding, an enlarged uterus, and postmenopausal bleeding. There may be a relationship to previous pelvic irradiation. At gross examination, the tumor is gray-tan and typically appears as a polypoid, fungating, papillary mass with a soft to firm consistency that fills the endometrial cavity (3). Hemorrhage or necrosis may be present. Histologic examination shows the epithelial component to be an adenocarcinoma of endometrial origin. As with adenosarcoma, there are homologous and heterologous components. The homologous components are stromal sarcoma and fibrosarcoma. The most common heterologous component is rhabdomyosarcoma. The staging is the same as for other uterine sarcomas (Table 1). Carcinosarcoma may metastasize to pelvic and paraaortic lymph nodes, pelvic soft tissues, the vagina, peritoneal surfaces, and the lungs. These tumors have variable signal intensity on T2-weighted MR images (14). On contrast-enhanced images, carcinosarcoma typically demonstrates heterogeneous enhancement, with the polypoid portion of the tumor showing intense enhancement (Fig 6). The differential diagnosis includes other sarcomas of the uterus and endometrioid cancer. Treatment typically consists of total abdominal hysterectomy with bilateral salpingo-oophorectomy and excision of extrauterine tumor. The 5-year survival rate is estimated at 18%–39% (13).
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Figure 6a. Carcinosarcoma in a 69-year-old woman. (a) Axial spin-echo T1-weighted MR image shows a mass with intermediate signal intensity that replaces the uterine corpus and cervix and extends through the internal os. (b) On a sagittal fast spin-echo T2-weighted MR image, the mass has high signal intensity and replaces the endometrial canal.
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Figure 6b. Carcinosarcoma in a 69-year-old woman. (a) Axial spin-echo T1-weighted MR image shows a mass with intermediate signal intensity that replaces the uterine corpus and cervix and extends through the internal os. (b) On a sagittal fast spin-echo T2-weighted MR image, the mass has high signal intensity and replaces the endometrial canal.
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Squamous Cell Carcinoma of the Cervix
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Tumors of the cervix that can manifest as large pelvic masses may be either benign (eg, leiomyoma, adenomyoma) or malignant (eg, squamous cell carcinoma, adenocarcinoma). Nearly 90% of all cervical carcinomas are squamous cell carcinoma. This tumor occurs most frequently between the ages of 45 and 55 years. More than 90% of squamous cell cervical cancer contains human papilloma virus DNA. Cervical cancer can occur at almost any age. The clinical features of invasive carcinoma of the cervix depend on the size of the lesion. The most common clinical symptom is vaginal bleeding. The tumor may manifest at gross examination as a fungating, ulcerating, or infiltrating tumor. At histologic analysis, the tumor typically appears as cords of neoplastic epithelium that infiltrate the fibrous stroma of the cervix. Stage I tumors are confined to the uterus, stage II tumors extend beyond the uterus but do not involve the pelvic wall or the lower third of the vagina, stage III tumors involve the pelvic wall or the lower third of the vagina, and stage IV tumors invade the bladder mucosa or rectum and extend beyond the true pelvis or form distant metastases (Table 2). MR imaging is useful in staging cervical cancer, particularly in the assessment of local extension and pelvic lymph nodes. Cervical carcinoma has relatively high signal intensity on T2-weighted MR images compared with the low signal intensity of the normal cervical stroma (Fig 7) (15). T2-weighted images and contrast-enhanced images are useful in the assessment of involvement of the bladder or rectum (15). The differential diagnosis includes endometrioid cancer, cancer of the vagina, and other rare sarcomas of the uterus. Treatment modalities for squamous cell carcinoma of the cervix include surgery, radiation therapy, and chemotherapy. The 5-year survival rate for patients in whom cervical cancer is detected early is approximately 91%; the overall survival rate for patients with cervical cancer is 69% (16).
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Figure 7a. Squamous cell carcinoma of the cervix in a 37-year-old woman. (a) On an axial spin-echo T1-weighted MR image, a mass with intermediate signal intensity is seen to arise from the uterine cervix. Note the enlarged external iliac nodes on the right side. (b) On a sagittal fast spin-echo T2-weighted MR image, the mass has intermediate signal intensity. The area of hyperintensity on T1- and T2-weighted images represents blood products. There is no extension of tumor to the bladder or rectum.
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Figure 7b. Squamous cell carcinoma of the cervix in a 37-year-old woman. (a) On an axial spin-echo T1-weighted MR image, a mass with intermediate signal intensity is seen to arise from the uterine cervix. Note the enlarged external iliac nodes on the right side. (b) On a sagittal fast spin-echo T2-weighted MR image, the mass has intermediate signal intensity. The area of hyperintensity on T1- and T2-weighted images represents blood products. There is no extension of tumor to the bladder or rectum.
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Fallopian Tube Adenocarcinoma
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Large pelvic masses may also originate from the fallopian tube. Diseases that can produce a large mass may be either benign (eg, leiomyoma, teratoma) or malignant (invasive adenocarcinoma). The most common malignant primary tumor of the fallopian tube is adenocarcinoma (3,17). This epithelial tumor accounts for 0.2%–0.5% of all primary female genital malignancies. Patients are typically 50–60 years old. The most common signs and symptoms include abnormal bleeding, vaginal discharge, and pain. At gross examination, the resected fallopian tube typically appears swollen due to intraluminal growth of a papillary or solid tumor (18). At histologic analysis, these tumors are composed of fine branching papillae. The staging is similar to that for ovarian cancer (Table 3). Stage I tumors are limited to one fallopian tube without penetration of the serosal surface, and no ascites is present. In stage II, the tumor invades one or both fallopian tubes with pelvic extension. In stage III, the tumor involves one or both fallopian tubes, with peritoneal implants outside the pelvis. Liver capsule metastases are considered indicative of stage III adenocarcinoma. Stage IV tumors are distant metastases (excluding peritoneal cavity metastasis). Fallopian tube adenocarcinoma is hyperintense on T2-weighted MR images, is hypointense on T1-weighted images, and demonstrates enhancement after the administration of gadopentetate dimeglumine (Fig 8) (19). The treatment strategy is similar to that for ovarian cancer. Patients typically undergo bilateral salpingo-oophorectomy and total abdominal hysterectomy, with aggressive debulking in patients with advanced tumor. The 5-year survival rate is 80% for patients with early disease and 20% for those with advanced disease (20).
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Figure 8a. Fallopian tube adenocarcinoma in a 76-year-old woman with a history of the disease. The patient had a recurrent large mass in the cul-de-sac that extended to the vaginal cuff and compressed the rectosigmoid colon. The mass was inseparable from small bowel loops. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates the mass with areas of high and intermediate signal intensity. (b) Axial contrast-enhanced T1-weighted MR image shows enhancement of the solid component of the mass with areas of necrosis.
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Figure 8b. Fallopian tube adenocarcinoma in a 76-year-old woman with a history of the disease. The patient had a recurrent large mass in the cul-de-sac that extended to the vaginal cuff and compressed the rectosigmoid colon. The mass was inseparable from small bowel loops. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates the mass with areas of high and intermediate signal intensity. (b) Axial contrast-enhanced T1-weighted MR image shows enhancement of the solid component of the mass with areas of necrosis.
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Ovarian Neoplasms
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Clear Cell Adenocarcinoma
Many ovarian tumors, both benign and malignant, can manifest as large pelvic masses. Clear cell adenocarcinoma is a subgroup of primary epithelial ovarian carcinoma. This tumor accounts for 5%–10% of all ovarian tumors. The mean age for affected patients is 52 years. There is an association with nulliparity, endometriosis, and endometrioid cysts. Presenting symptoms include abdominal discomfort, pain, and distention and gastrointestinal symptoms. At gross examination, the tumor is seen to consist of both solid and cystic components (3). Most are unilocular cystic masses. The histologic appearance may be solid, organoid, or tubulopapillary. The cells are clear and polyhedral with high-grade nuclei. The staging of ovarian cancer is outlined in Table 4. The cystic components are hyperintense on T2-weighted MR images and have variable signal intensity on T1-weighted images (21). The solid components typically have intermediate to high signal intensity on T2-weighted images (Fig 9). In cystic primary ovarian lesions, gadolinium-based contrast enhancement of the solid component has been shown to be helpful in making the diagnosis (21). The presence of ascites and peritoneal enhancement is important in predicting malignancy (22). The differential diagnosis includes other types of epithelial tumor of the ovary, primary tumors, and metastatic disease. Clear cell adenocarcinoma is treated with surgery and chemotherapy. The 5-year survival rate for patients with stage I clear cell adenocarcinoma is 80%–90%. Most patients present with stage I disease (23).
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Figure 9a. Clear cell carcinoma of the ovary in a 41-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates a hyperintense mass. (b) On an axial contrast-enhanced spin-echo T1-weighted MR image, the mass demonstrates heterogeneous enhancement.
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Figure 9b. Clear cell carcinoma of the ovary in a 41-year-old woman. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates a hyperintense mass. (b) On an axial contrast-enhanced spin-echo T1-weighted MR image, the mass demonstrates heterogeneous enhancement.
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Metastatic Cancer
Large adnexal masses may be present secondary to metastatic disease. Approximately 3% of ovarian tumors are due to metastases, most commonly from the breast, stomach, colon, and other female organs. Krukenberg tumors are characterized by ovarian enlargement secondary to signet-ring cell carcinoma that has metastasized to the ovary, most commonly from the stomach and breast (Fig 10). Other metastases to the ovary (eg, from renal cell carcinoma) are very rare (24). In renal cell carcinoma metastatic to the ovaries, microscopic examination shows proliferation of atypical polygonal epithelial cells with pleomorphic, hyperchromatic central nuclei and abundant clear cell cytoplasm. To our knowledge, the MR imaging appearance of this unusual metastatic lesion has not been reported. In our experience, the tumor is isointense relative to muscle and demonstrates variable enhancement on T1-weighted images, with heterogeneous signal intensity on T2-weighted images (Fig 11).
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Figure 10a. Metastatic breast cancer in the ovary in a 66-year-old woman. (a) Axial fast spin-echo T2-weighted MR image shows a left adnexal mass with both cystic and solid components and a right adnexal mass that is mostly solid. (b) On an axial contrast-enhanced spin-echo T1-weighted MR image, there is enhancement of the solid components of the adnexal masses.
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Figure 10b. Metastatic breast cancer in the ovary in a 66-year-old woman. (a) Axial fast spin-echo T2-weighted MR image shows a left adnexal mass with both cystic and solid components and a right adnexal mass that is mostly solid. (b) On an axial contrast-enhanced spin-echo T1-weighted MR image, there is enhancement of the solid components of the adnexal masses.
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Figure 11a. Metastatic renal cell carcinoma in the right ovary in a 62-year-old woman. The patient had a history of supracervical hysterectomy, which had revealed this tumor. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates a mass with heterogeneous signal intensity. (b) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates variable enhancement.
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Figure 11b. Metastatic renal cell carcinoma in the right ovary in a 62-year-old woman. The patient had a history of supracervical hysterectomy, which had revealed this tumor. (a) Sagittal fast spin-echo T2-weighted MR image demonstrates a mass with heterogeneous signal intensity. (b) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates variable enhancement.
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Peritoneal Neoplasms
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Peritoneal diseases that can manifest as masses include mesothelial tumors, pseudomyxoma peritonei, and desmoid tumors.
Multicystic Mesothelioma
Multicystic mesothelioma is a rare neoplasm that occurs predominantly in women of reproductive age, with a strong predilection for the pelvic viscera (25). Many patients are asymptomatic, and the tumor is typically found incidentally, but symptoms of variable intensity can occur depending on the size of the tumor. There is usually a history of prior abdominal surgery, pelvic inflammatory disease, or endometriosis. At histologic analysis, these tumors are lined by a single layer of flat to cuboidal mesothelial cells, without the presence of smooth muscle (3). At MR imaging, these lesions typically appear as thin-walled, multicystic lesions. The cystic component has intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. The thin walls demonstrate minimal contrast enhancement (Fig 12) (26).
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Figure 12a. Multicystic mesothelioma in a 54-year-old woman. (a) Axial fast spin-echo T2-weighted MR image shows a mass with areas of high and intermediate signal intensity. There is mass effect on the sigmoid colon. (b) Axial contrast-enhanced T1-weighted MR image demonstrates minimal enhancement of the multiloculated mass.
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Figure 12b. Multicystic mesothelioma in a 54-year-old woman. (a) Axial fast spin-echo T2-weighted MR image shows a mass with areas of high and intermediate signal intensity. There is mass effect on the sigmoid colon. (b) Axial contrast-enhanced T1-weighted MR image demonstrates minimal enhancement of the multiloculated mass.
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Pseudomyxoma Peritonei
Pseudomyxoma peritonei typically has the appearance of a multicystic mass that can mimic multicystic mesothelioma. It is characterized by the accumulation of mucinous fluid in the peritoneum and retroperitoneum (27). Pseudomyxoma peritonei represents a form of intraperitoneal spread of mucin-secreting tumors. This condition is most often associated with tumors of the appendix (adenoma, adenocarcinoma) and ovaries (benign or malignant mucinous tumors) (27). The most common clinical manifestation in female patients is an ovarian mass. Signs and symptoms include abdominal pain, distention, nausea, vomiting, and fatigue. The disease may cause obstruction of the ureters or of venous return from the lower extremities. Gross examination typically reveals a thick, yellow-gray mucoid material. Histologic examination shows mucin-producing cells associated with well-differentiated columnar epithelium. The mucin has high signal intensity on T2-weighted MR images and low signal intensity on T1-weighted images (Fig 13) (28). Patients may undergo surgical debulking.
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Figure 13a. Pseudomyxoma peritonei in a 67-year-old woman. (a) Axial fast spin-echo T2-weighted MR image demonstrates a mostly high-signal-intensity mass. (b) Axial contrast-enhanced fat-saturated T1-weighted MR image shows enhancement of the solid components of the mass.
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Figure 13b. Pseudomyxoma peritonei in a 67-year-old woman. (a) Axial fast spin-echo T2-weighted MR image demonstrates a mostly high-signal-intensity mass. (b) Axial contrast-enhanced fat-saturated T1-weighted MR image shows enhancement of the solid components of the mass.
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Desmoid Tumor
Desmoid tumors may be located in the peritoneum and may manifest as a large pelvic mass. They may occur at any age but have a peak prevalence in patients between 20 and 30 years of age. Clinical symptoms are masked by the slow growth of the tumor. The most common clinical manifestation in female patients is an ovarian mass. Desmoid tumors may be extraabdominal (typically in the shoulder, chest wall, thigh, and back), abdominal (typically in the aponeurotic structures of the abdominal wall), or intraabdominal (typically in the mesentery and the pelvic walls). Intraabdominal desmoid tumors are commonly associated with Gardner syndrome. At gross examination, these masses are typically firm and unencapsulated with coarse white trabeculae that simulate scar tissue. At histologic analysis, desmoid tumors consist of elongated spindle-shaped cells separated by dense bands of collagen. These tumors are hypointense on T1-weighted MR images and have variable signal intensity on T2-weighted images (Fig 14) (29). Desmoid tumors are treated with surgical resection. They have a high recurrence rate, and adjunct radiation therapy has been recommended.
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Figure 14a. Locally invasive pelvic desmoid tumor in a 25-year-old woman. (a) Axial fast spin-echo T2-weighted MR image demonstrates a hypointense mass. (b) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates only minimal enhancement.
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Figure 14b. Locally invasive pelvic desmoid tumor in a 25-year-old woman. (a) Axial fast spin-echo T2-weighted MR image demonstrates a hypointense mass. (b) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates only minimal enhancement.
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Gastrointestinal Neoplasms
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Tumors of the gastrointestinal tract, whether from the large or small bowel, may also manifest as large pelvic masses. Such tumors include primary rectal carcinoma and gastrointestinal stromal tumors (GISTs) (30).
Rectal Cancer
Colorectal cancer is the second most common form of visceral cancer. Approximately 40,000 cases of rectal cancer are diagnosed each year in the United States. The lifetime risk for developing a colorectal malignancy is approximately 5.9% in the general U.S. population (30). About one-third of colorectal cancers occur in the rectum. There is a peak prevalence during the 7th decade of life. At gross examination, rectal adenocarcinoma appears as a polypoid mass that increases in size to finally encircle the bowel wall. Adenocarcinoma of the rectum typically manifests with bleeding or a change in bowel habits. At histologic analysis, these tumors are mostly well- to moderately differentiated adenocarcinomas (30). The glands demonstrate high mitotic indexes. The staging of rectal cancer is outlined in Table 5. On T1-weighted MR images, the tumor is isointense relative to the rectum; on T2-weighted images, it is hyperintense. There is enhancement following administration of gadopentetate dimeglumine (Fig 15) (15,31). The differential diagnosis for rectal cancer includes soft-tissue sarcoma, GIST, and extension of tumor from adjacent organs. Inflammatory changes may mimic rectal cancer. The 5-year survival rate is over 90% for patients with stage I rectal cancer, 70%–85% for those with stage II disease, and less than 65% for those with stage III disease and approaches 0% for patients with stage IV rectal cancer (32).
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Figure 15a. Locally advanced rectal cancer in a 68-year-old woman. There was a large mass that extended posteriorly to the sacrum, the pelvic sidewall, the piriformis muscles, and the posterior wall of the vagina. (a) Sagittal fast spin-echo T2-weighted MR image shows a hyperintense mass. (b) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates heterogeneous enhancement.
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Figure 15b. Locally advanced rectal cancer in a 68-year-old woman. There was a large mass that extended posteriorly to the sacrum, the pelvic sidewall, the piriformis muscles, and the posterior wall of the vagina. (a) Sagittal fast spin-echo T2-weighted MR image shows a hyperintense mass. (b) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates heterogeneous enhancement.
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Gastrointestinal Stromal Tumor
GISTs account for less than 1% of all gastrointestinal cancers. An estimated 150 new cases are diagnosed each year, with an annual incidence in the U.S. of 0.07 cases per 100,000 persons (33). GISTs constitute the largest subset of mesenchymal tumors of the gastrointestinal tract with expression of c-Kit. GISTs can affect patients of any age, although most patients are over 40 years old. Patients may present with bleeding, obstruction, abdominal pain, jaundice, weight loss, or peritonitis. Most cases of GIST (70%) arise from the stomach, with 20%–30% in the small intestine and less than 10% each in the esophagus, colon, and rectum.
At histologic analysis, stromal fibroblasts and blood vessels are intermingled with neoplastic smooth muscle cells. GISTs may contain islands of fat, bone, or cartilage (33). The staging of GISTs is outlined in Table 6. These tumors have been reported to have low signal intensity on T1-weighted MR images and intermediate intensity on T2-weighted images and to demonstrate marked enhancement following the administration of gadopentetate dimeglumine (Fig 16) (34). The differential diagnosis for GIST includes primary adenocarcinoma of the bowel. The prognosis for affected patients is poor. The 5-year survival rate for patients with GIST of the stomach is 50%–60%; for those with GIST of the small bowel, it is 40%–50% (35).
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Figure 16a. GIST of the rectovaginal septum in a 61-year-old woman. (a) Axial spin-echo T1-weighted MR image demonstrates a mass with intermediate signal intensity. (b) Sagittal fast spin-echo T2-weighted MR image demonstrates the mass in the rectovaginal septum. (c) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates marked enhancement.
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Figure 16b. GIST of the rectovaginal septum in a 61-year-old woman. (a) Axial spin-echo T1-weighted MR image demonstrates a mass with intermediate signal intensity. (b) Sagittal fast spin-echo T2-weighted MR image demonstrates the mass in the rectovaginal septum. (c) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates marked enhancement.
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Figure 16c. GIST of the rectovaginal septum in a 61-year-old woman. (a) Axial spin-echo T1-weighted MR image demonstrates a mass with intermediate signal intensity. (b) Sagittal fast spin-echo T2-weighted MR image demonstrates the mass in the rectovaginal septum. (c) On an axial contrast-enhanced T1-weighted MR image, the mass demonstrates marked enhancement.
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Soft-Tissue Neoplasms
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Soft-tissue neoplasms of the pelvis include vascular tumors (hemangiopericytoma, angiosarcoma), skeletal muscle tumors (rhabdomyosarcoma), lipid tumors (liposarcoma), neural tumors (neurofibroma, neurosarcoma), and smooth muscle tumors (leiomyosarcoma).
Hemangiopericytoma
Hemangiopericytomas are rare neoplasms and may occur anywhere in the body. The tumor may manifest in patients of any age, although most patients are 40–50 years old. Hemangiopericytomas are most commonly located in the lower extremities or retroperitoneum. They manifest clinically as a painless mass. Mass effect from the tumor on adjacent structures may cause symptoms secondary to constipation, hydronephrosis, or nerve impingement. Gross examination reveals a capsule with a surrounding dense venous plexus (36). At histologic analysis, hemangiopericytomas consist of capillary channels surrounded by spindle-shaped cells (3). Stage I hemangiopericytomas are low-grade, well- to moderately differentiated tumors (all pelvic sarcomas are considered deep tumors) of any size. Stage II tumors are low-grade or deep tumors larger than 5 cm or high-grade tumors of any size and are poorly differentiated or undifferentiated and superficial. Stage III tumors are high-grade, poorly differentiated or undifferentiated deep tumors larger than 5 cm. Stage IV tumors are metastatic tumors of varying grade and size (Table 7). Hemangiopericytomas may recur or may metastasize to the lungs or bone. The mass has intermediate signal intensity on T1-weighted MR images and high signal intensity on T2-weighted images (Fig 17). The solid components of the tumor enhance with the administration of gadopentetate dimeglumine (36). The 5-year survival rate for patients with hemangiopericytoma is 70% (37).
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Abstract
LEARNING OBJECTIVES
